Facile synthesis of positively charged monosubstituted α- and γ-cyclodextrins for chiral resolution of anionic racemates

New positively charged monosubstituted α- and γ-cyclodextrins at the primary face were synthesized in good yields by displacement of the monotosylates of α- and γ-cyclodextrin with amine, alkylamines or alkylimidazoles. The influence of CD’s cavity size on the resolution abilities of CD derivatives towards model analytes, that is, dansyl amino and carboxylic acids, were investigated. Results show that the formation of the inclusion complex might play an important role in chiral recognition, in that cationic γ-CD derivatives gave better resolution abilities than their α- and γ-CD analogues, presumably due to tight fit between CD hosts and the anionic guest racemates.

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Mono-6A-N-ammonium-6A-deoxy-α-cyclodextrin chlorideC36H62NClO29[α]D = +74.9 (c 1.0, water)Source of chirality: α-cyclodextrin

Mono-6A-N-ammonium-6A-deoxy-γ-cyclodextrin chlorideC48H82NClO31[α]D = +102.8 (c 1.0, water)Source of chirality: γ-cyclodextrin

Mono-6A-(1-butyl-3-imidazolium)-6A-deoxy-α-cyclodextrin chlorideC43H71N2ClO29[α]D = +83.6 (c 1.0, water)Source of chirality: α-cyclodextrin

Mono-6A-(1-methyl-3-imidazolium)-6A-deoxy-γ-cyclodextrin chlorideC52H85N2ClO39[α]D = +125.4 (c 1.0, water)Source of chirality: γ-cyclodextrin

Mono-6A-propylammonium-6A-deoxy-γ-cyclodextrin chlorideC51H88NClO39[α]D = +131.2 (c 1.0, water)Source of chirality: γ-cyclodextrin